The invention relates to a baffle seal (also referred to as labyrinth seal) for use in a balance. Baffle seals of this kind have one or more sleeve-shaped ring elements in a stationary position around an opening in a housing that is to be sealed, and a cover cap with one or more sleeve-shaped rings that is axially movable in relation to the one or more sleeve-shaped ring elements. In particular, a balance with the baffle seal has a force-transmitting member reaching through the housing for the introduction of the weighing load. Beyond the baffle seal itself, the invention also relates to a balance that is equipped with a baffle seal meeting the foregoing description.
Baffle seals are often used to seal the housings of machines or instruments in which a force- or torque-transmitting mechanical element extends through an opening in the housing. The use of baffle seals in roller bearings is known, e.g., from Dubbel, Taschenbuch für den Maschinenbau, 17. Auflage, Springer-Verlag, Berlin 1990, page G87, to prevent dirt from entering as well as to prevent lubricant from escaping. As FIG. 31a of the reference just mentioned illustrates, a baffle seal consists of two seal parts, where each part has at least one tubular ring and the rings are slid over each other, arranged concentrically with the opening of the housing. This arrangement creates a narrow baffled air path which allows a friction-free axial or rotary movement of the two seal parts in relation to each other and which prevents at the same time that substances could enter into or escape from the housing that is to be sealed.
The drawing FIG. 1 attached hereto shows a part of a balance with a housing 30. Extending through an opening 31 of the housing, the balance has a transmitting member 20 that is axially movable inside a body 40 and serves to transmit a force originating from a weighing load to the measuring cell of the balance. Above the opening 31, a body 40 is arranged with a device 42 that functions to elastically expand the circumference. The illustrated arrangement, which is the subject of the European Patent Application EP A 1 146 322, has a cover cap 1 in the shape of an inverted cup that is set on a load button 13 of a hub element 21. The latter transmits the weight force to a conical peg 22 that is coupled to the measuring cell.
The cover cap 1 has a sleeve-shaped or tubular-shaped outer ring 10 as well as a sleeve-shaped or tubular-shaped inner ring 12. The outer ring 10 and inner ring 12 run coaxial, have different diameters and, consequently, define a hollow-space 14 between each other. A cup-shaped sealing cap 2 is arranged in a stationary position concentric to the opening 31 of the housing 30. The sealing cap 2 has a ring element 110 directed towards the cover cap 1 and dimensioned with an appropriate diameter so that, with the cover cap 1 set in place, the ring element 110 extends into the hollow space 14 and thereby forms a baffled air path 100 that undulates up and down resembling a concentric wave pattern.
For the cleaning of the balance, it would often be desirable if the baffled air path 100 could be completely closed off. Particularly in automated weighing processes, it would furthermore be advantageous if the force-transmitting member 20 could be arrested, so that the measuring cell would not be subjected to unwanted forces during breaks in the measuring process.
In the illustrated arrangement of FIG. 1, the two functions of closing the baffled air path and arresting the force-transmitting member are performed advantageously by a device 42 that surrounds the body 40 and resembles an inflatable tire which can be expanded as well as returned from the expanded state in a controlled manner. In the expanded condition, the tire-shaped device 42 presses against the inner ring 12 of the cover cap 1, whereby the baffled air path 100 is tightly closed off and the cover cap 1 is immobilized. After the air path 100 has been closed off in this manner, the balance can be cleaned with a jet of water or compressed air without risking that dirt, water, or residues of weighed substances could enter the housing 30 through the baffled air path 100. At the same time, the transmitting member 20 is immobilized, so that load fluctuations cannot be transmitted to the measuring cell of the balance.
The cover cap 1 can be taken off to expose the parts underneath for cleaning. However, as can be clearly seen in FIG. 1, the space 15 between the tire-shaped device 42 and the ring element 110 of the stationary sealing cap 2 is hardly accessible, so that residues accumulated in the space 15 are hard to remove. Likewise, residues settled between the sealing cap 2 and the housing 30 are difficult to remove. Furthermore, the way in which the sealing cap 2 is installed makes the entire arrangement relatively expensive to manufacture.